Large-scale Upwelling Research Articles

The Obir caves adjacent to the Periadriatic Fault in southern Austria: Uplifted hypogene caves formed by carbonic acid speleogenesis

Hypogene karst caves, formed independently of surface processes, have garnered increasing attention in recent decades, revealing a wider distribution than previously assumed. While most studies have relied on morphological observations, this research combines morphological and geochemical approaches to present new insights from the Obir caves in the Northern Karawank Mountains, Austria. These caverns, discovered during mining activities, lack natural entrances and developed along a prominent master horizon about 500 m above the current spring level. Notably, large shafts within the caves originate in narrow fissures and terminate blindly at the top, also suggesting a phreatic regime during their formation, with some areas being modified by vadose waters later on. A comprehensive study of drill cores indicates a stable isotope halo in the first few centimeters of the wall rock, characterized by significantly depleted δ13C and moderately depleted δ18O values compared to the pristine limestone, accompanied by bleaching of the host rock. This geochemical evidence of wall rock alteration is only present where the original phreatic solutional morphology is preserved and absent where vadose waters resulted in rugged cave wall surfaces.Considering the lack of evidence for the involvement of sulfuric acid or thermal waters, the formation of the Obir caves is attributed to carbonic acid speleogenesis. This interpretation is supported by the observed strong C isotope shift in the wall rock and the presence of CO2-bearing springs both north and south of the Periadriatic Fault. In contrast to previous studies of carbonic acid speleogenesis suggesting large-scale upwelling of aggressive waters, we propose an alternative mechanism: the injection of carbon dioxide gas into limestone situated in the phreatic zone. These injections likely occurred along subvertical tectonic fissures, triggered by the tectonic transpression of the Northern Karawank Mountains during the middle Miocene. Subsequent tectonic uplift and the incision of valleys led to a drop in the groundwater table, widespread collapse of larger cave rooms and localized vadose overprint.This study highlights the strength of combining mega- to the microscale cave morphological observations with systematic geochemical analyses of wall rock alteration in identifying caves formed by carbonic acid speleogenesis.

Geochronological and geochemical study of the Late Carboniferous volcanic drilling cores from the Piedmont of the Hala'alate Mountain in West Junggar: Implications for stratigraphic division and tectonic evolution

The West Junggar tectono-magmatic processes are critical for reconstructing the amalgamation history of the Central Asian Orogenic Belt (CAOB). However, the lack of consensus regarding the geochronology, petrogenesis, and tectonic setting of the complex igneous rocks poses a challenge to comprehending the Late Paleozoic tectonic evolution of West Junggar. This study focuses on systematic geochronological and geochemical research of well-preserved drill cores from the Piedmont of the Hala'alate Mountain, including rhyolite, felsic tuff, basalt, and andesite. The ages of these rocks in Late Carboniferous (310–301 Ma) are constrained by zircon UPb dating, excluding them from the Jiamuhe Formation of the Early Permian. The rhyolites and felsic tuffs exhibit apparent affinity to the A-type granite series, characterized by high total alkali and FeOT/MgO values. Plagioclase controls the main residual facies and depleted isotopic compositions (εHf(t) = +10.2 to +13.4; εNd(t) = +7.6 to +8.1), indicating that the magma source originated from the partial melting of juvenile continental materials in an extensional background. The basalts and andesites display high LILEs/LREEs, LILEs/HFSEs ratios, along with low HFSEs, which correspond to arc-affinity geochemical compositions. The high zircon εHf(t) (+7.5 to +14.3) and whole-rock εNd(t) (+7.8 to +7.9) values indicate a depleted pyroxene-rich mantle source modified by metasomatic slab-derived fluids. This implies a large-scale upwelling of mantle materials driven by the overlying lithospheric crustal thinning. Combining the temporal variations of crustal thickness recorded by the Sr/Y and (La/Yb)N ratios in igneous rocks, the tectonic processes of West Junggar during the Carboniferous to Early Permian can be divided into three stages. The first stage involves sustained subduction processes from 350 Ma to 320 Ma, followed by the closure of the oceanic crust and collision orogenesis from 320 Ma to 310 Ma. Finally, and a post-collision extension setting occurred after 310 Ma.

Influence of Upper-Troposphere Stratification and Cloud-Radiation Interaction on Convective Overshoots in the Tropical Tropopause Layer

AbstractIt is still debated whether radiative heating observed in the tropical tropopause layer (TTL) is balanced primarily by cooling from convective overshoots, as in an entrainment layer, or by adiabatic cooling from large-scale eddy-driven upwelling. In this study, three-dimensional cloud-resolving model simulations of radiative-convective equilibrium were carried out with three different cloud microphysics schemes and 1-km horizontal resolution. We demonstrate that overshooting cooling in the TTL can be strongly modulated by upper-troposphere stratification. Two of the schemes produce a hard-landing scenario in which convective overshoots reach the TTL with frequent large vertical velocity leading to strong overshooting cooling (~ −0.2 K day-1). The third scheme produces a soft-landing scenario in which convective overshoots rarely reach the TTL with large vertical velocity and produce little overshooting cooling (~ −0.03 K day-1). The difference between the two scenarios is attributed to changes in the upper-troposphere stratification related to different atmospheric cloud radiative effects (ACRE). The microphysics scheme that produces the soft-landing scenario has much stronger ACRE in the upper troposphere leading to a ~3K warmer and more stable layer which acts as a buffer zone to slow down the convective updrafts. The stratification mechanism suggests the possibility for the ozone variation or eddy-driven upwelling in the TTL to modulate convective overshoots. We further test the sensitivity of overshooting cooling to changes in model resolution by increasing the horizontal resolution to 100 m. The corresponding change of overshooting cooling is much smaller compared with the difference between the hard-landing and soft-landing scenarios.

Petrogenesis and geodynamic setting of the Late Carboniferous granodiorite porphyry in Miaoergou pluton, southern West Junggar

位于西准噶尔南部的庙尔沟岩体主体由碱长花岗岩和少量紫苏花岗岩组成。本文在前人工作基础上，以岩体东南边缘新发现的花岗闪长斑岩为研究对象，开展岩石学、年代学和Hf同位素以及全岩地球化学研究，确定花岗闪长斑岩形成时代、揭示岩石成因类型及源区属性、探讨其与碱长花岗岩和紫苏花岗岩岩浆演化成因联系及其形成的深部动力学过程。锆石U-Pb定年结果显示，花岗闪长斑岩形成于317.4±1.9Ma，为晚石炭世早期岩浆活动的产物，明显早于紫苏花岗岩（~307Ma）和碱长花岗岩（~303Ma）。岩石地球化学数据表明，花岗闪长斑岩具有较高硅、中等铝，贫钙、铁、镁，富集Rb、K、Th、U，强烈亏损Nb、Ta、Ti的特征，为钙碱性弱过铝质I型花岗岩；紫苏花岗岩更多的表现出钙碱性-高钾钙碱性镁质I型紫苏花岗岩特征；碱长花岗岩为碱性准铝质-弱过铝质A型花岗岩。锆石Hf同位素分析结果表明，花岗闪长斑岩、紫苏花岗岩和碱长花岗岩均具有高正的ε_Hf（t）值（+11.6~+15.8）和年轻的二阶段模式年龄（325~600Ma），表明其原始岩浆主要起源于亏损地幔新衍生的年轻地壳物质。综合分析认为，庙尔沟岩体花岗闪长斑岩形成于晚石炭世早期洋壳俯冲背景，由底侵的、受流体交代的幔源基性岩浆与其诱发的年轻下地壳酸性岩浆在深部混合而成。紫苏花岗岩和碱长花岗岩形成于弧后伸展背景，前者是伸展初期继续底侵于下地壳的幔源玄武质岩浆降温释放大量的水和热诱使早期侵位于下地壳的镁铁质岩石再次发生部分熔融的产物，后者是伸展后期大规模软流圈地幔上涌底垫加热年轻中下地壳使其部分熔融而成。;The Miaoergou pluton, located in southern West Junggar, is mainly composed of alkali-feldspar granites with small amount of charnockites. On the basis of previous researches, this paper mainly focuses on the newly discovered granodiorite porphyry in southwestern margin of the Miaoergou pluton. A comprehensive study of petrographical, zircon U-Pb geochronological and in-situ Hf isotopic, whole-rock geochemical analyses were carried out to determine its diagenetic age and reveal the petrogenesis, the nature and composition of the magma source of this porphyry, and furthermore, to discuss the genetic relationships among the granodiorite porphyries, alkali-feldspar granites and charnockites and their geodynamic processes. LA-ICP-MS zircon U-Pb dating for the granodiorite porphyry yielded crystallization age of 317.4±1.9Ma, defining an early Late Carboniferous magmatic event in southern West Junggar, which is significantly earlier than the ages of charnockites (~307Ma) and alkali-feldspar granites (~303Ma). The geochemical characteristics indicate that the studied granodiorite porphyries belong to cal-alkaline weakly peraluminous I-type granite, and are characterized by slightly high silicon, medium aluminum, but low ferrum, calcium and magnesium, and also enrichment in Rb, K, Th, U with pronounced negative Nb, Ta and Ti anomalies. The charnockites possess calc-alkaline to high-K calc-alkaline magnesian I-type charnockite affinities, which were previously considered A-type granites by some geologists, while alkali-feldspar granites belong to alkaline metaluminous to weakly peraluminous A-type granites. In-situ zircon Hf isotope analyses show that these granites have high positive ε_Hf(t) values (+11.6~+15.8) and very young two-stage Hf model ages of 325~600Ma, indicating that the magma was sourced from juvenile crust originated from depleted mantle during the Late Neoproterozoic to Early Carboniferous period. In association with previous analysis, it is proposed that the Miaoergou granodiorite porphyries were formed in an oceanic crust subduction setting during early Late Carboniferous. They are probably the products of the acidic magma formed by partial melting of the juvenile lower crust and mixed with the underplated basaltic magma derived from the fluid metasomatic mantle wedge in the deep crust to some extent. Both the charnockites and alkali-feldspar granites were formed in a back-arc extensional setting related to the northwestward subduction of the Junggar oceanic crust. The charnockites may be generated by re-melting of juvenile lower crust mafic rocks, probably triggered by addition of water and heat released from cooling of underplated depleted mantle-derived basaltic magma during the incipient rifting stage of the back-arc basin, and the alkali-feldspar granites may be generated by partial melting of the juvenile middle-lower crust induced by the large-scale upwelling of asthenosphere during the later stage of the back-arc extension.

Ocean color as a proxy to predict sea surface salinity in the Banda Sea

Salinity is an important ocean parameter that greatly influences physical, chemical, and biological ocean properties and processes. Salinity combines with sea temperature and chlorophyll-a (Chl-a) that mostly sourced from remote sensing-based measurements can reveal ocean quality and supports fisheries. However, the satellite-derived Sea Surface Salinity (SSS) dataset (∼ 9 years) is not as temporally adequate as SST and Chl-a datasets (∼3 decades) and thus, preventing a comprehensively spatio-temporal analysis of this water quality aspect. Since (SSS) can be approximated using satellite-derived ocean color products having the similar temporal length of datasets to the available SST and Chl-a datasets, predicted SSS can be produced from these ocean color products to fill the gap of the existing SSS dataset. This study aims to estimate the SSS from ocean color products of Aqua-MODIS satellite with a spatial and temporal resolution of 4 km and 8-daily by developing an empirical model. The ocean color data used were remote sensing reflectance (Rrs) of blue, green and red wavelengths (412, 433, 469, 488, 531, 547, 555, 645, 667 and 678 nm). The absorption coefficients due to detritus material non-algae, Gelbstof and CDOM (ADG) at 443 nm and the absorption coefficient due to phytoplankton (APH) at 443 nm data were also used. The Banda Sea was chosen due to its large-scale upwelling system (∼300 km × 300 km) that providing an important ocean process related to fishery and the availability of in-situ salinity measurements (i.e. CTD casts from series of Research Vessel (R/V) Baruna Jaya III, VII and VIII cruises and Argo floats), which a part of these datasets will be used to validate predicted SSS. Results showed that of all ocean color parameters tested, ADG at 443 nm was strongly correlated with in-situ SSS through the polynomial order 5 regression equation with a high R2 of 0.94 and a low RMES value of 0.101 PSU. Although this empirical model has high accuracy, but based on RMSE analysis results from various locations within and outside the Banda Sea that influenced by the Pacific and the Indian ocean water masses indicates that this model actually good to predict in-situ SSS only for a narrow range SSS of 33.4-34.5 PSU. Nevertheless, this model has a limitation, it is still can be used for predicting and mapping the SSS for Banda Sea as well as for most of the Indonesian waters. The long-term meteorological SSS map (2003-2017) derived by this model together with the SST and Chl-a maps can show clearly the upwelling phenomena of the Banda Sea, which occurred during the southeast monsoon (June-July-August, JJA). This study proves that ocean color data from Aqua-MODIS satellite can be applied to estimate and to map the SSS for most of the Indonesian waters, but validations for this model is still needed

Intensification of Atlantic and Pacific Large-Scale Upwelling under Recent Climate Conditions

Using satellite data on the sea surface temperature since 1985 (with a resolution of 0.25° × 0.25°) and the sea surface wind since 1992 (on a grid of 0.25° × 0.25°), the parameters of the low-frequency variability of the fields characterizing the intensity of the Canary, Benguela, Californian, Peruvian and Chilean upwellings have been analyzed. It is shown that the large-scale wind-driven upwellings listed above are intensifying. The contributions of the offshore wind and varying vertical velocities caused by space inhomogeneity of the wind field into this intensification are assessed for each upwelling.

High oxygen fugacity magma: implication for the destruction of the North China Craton

The mechanism of lithospheric removal and destruction of the North China Craton (NCC) has been hotly debated for decades. It is now generally accepted that the subduction of the (Paleo)-Pacific plate played an important role in this process. However, how the plate subduction contributed to the craton destruction remains unclear. Here we report high oxygen fugacity (fO2) characteristics of the Yunmengshan granite, e.g., hematite–magnetite intergrowth supported by zircon Ce4+/Ce3+ ratios and apatite Mn oxygen fugacity indicator. High fO2 magmas are widely discovered in Late Mesozoic (160–130 Ma) adakitic rocks in central NCC. The origin of high fO2 magma is likely related to the input of the “oxidized mantle components”, which shows a close connection between plate subduction and destruction of the craton. The research area is ~ 1500 km away from the current Pacific subduction zone. Considering the back-arc extension of Japan Sea since the Cretaceous, this distance may be shortened to ~ 800 km, which is still too far for normal plate subduction. Ridge subduction is the best candidate that was responsible for the large scale magmatism and the destruction of the NCC. Massive slab-derived fluids and/or melts were liberated into an overlying mantle wedge and modified the lithospheric mantle. Rollback of the subducting plate induced the large-scale upwelling of asthenospheric mantle and triggered the formation of extensive high fO2 intraplate magmas.

Ca. 780 Ma OIB-like mafic dykes in the Western Jiangnan orogenic Belt, South China: evidence for large-scale upwelling of asthenosphere beneath a post-orogenic setting

ABSTRACT Post-collisional alkaline mafic rocks record significant information regarding crust–mantle interaction in the subduction channel and provide an excellent opportunity to investigate the mechanism of transition from pre-collisional to post-collisional magmas. In this contribution, we present whole-rock major and trace element and radiogenic isotope data obtained from alkaline mafic dykes in the Guzhang-Anjiang areas in the southwestern Jiangnan orogenic belt (JOB), South China. LA–ICP–MS U–Pb zircon dating of four representative samples yields a consistent age of ~780 Ma. These mafic dykes are characterized by large variations in SiO2 (42.4–54.1 wt.%) and MgO (2.2–15.0 wt.%), alkalis (K2O+Na2O = 1.96–11.19 wt.%), Nb (17.55–49.62 ppm) and Ta (1.15–3.26 ppm). They exhibit ocean island basalt (OIB)-like geochemical features, which are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) relative to heavy rare earth elements (HREEs) and by positive zircon εHf(t) (+1.86 to +5.14) and whole-rock εNd(t) (+0.31 to +1.80) values. All these geochemical characteristics suggest these dykes were derived from a small degree (2–5%) of partial melting of an asthenospheric mantle source that had previously been modified by earlier subduction processes. Based on the previous reports and present study, we infer that three periods of Neoproterozoic basaltic magmatism occurred in the western Jiangnan Orogen, and constrain the time of the tectonic regime transformation at ~830, and at ~780 Ma. The source of these basaltic rocks varied in composition spatially and evolved with time. The ~780 Ma OIB-like rocks in this study serve as an important indicator of large-scale upwelling of the asthenospheric mantle and the transition from orogenic to post-orogenic tectonic setting.

The Thermally Driven Ocean Circulation with Realistic Bathymetry

AbstractThe global circulation driven solely by relaxation to an idealized surface temperature profile and to interior mixing is examined. Forcing by winds and evaporation/precipitation is excluded. The resulting circulation resembles the observed in many ways, and the overturning is of similar magnitude. The overturning is driven by large-scale upwelling in the interior (which is relatively large, because of the use of a constant mixing coefficient). The compensating downwelling occurs in the northern North Atlantic and in the Ross and Weddell Seas, with an additional, smaller contribution from the northern North Pacific. The latter is weaker because the Bering Strait limits the northward extent of the flow. The downwelling occurs in frictional layers near the boundaries and depends on the lateral shear in the horizontal flow. The shear, in turn, is linked to the imposed surface temperature gradient via thermal wind, and as such, the downwelling can be reduced or eliminated in selected regions by removing the surface gradient. Doing so in the northern North Atlantic causes the (thermally driven) Antarctic Circumpolar Current to intensify, increasing the sinking along Antarctica. Eliminating the surface gradient in the Southern Ocean increases the sinking in the North Atlantic and Pacific. As there is upwelling also in the western boundary currents, the flow must increase even more to accomplish the necessary downwelling. The implications of the results are then considered, particularly with respect to Arctic intensification of global warming, which will reduce the surface temperature gradient.

Inverse-model estimates of the ocean's coupled phosphorus, silicon, and iron cycles

Abstract. The ocean's nutrient cycles are important for the carbon balance of the climate system and for shaping the ocean's distribution of dissolved elements. Dissolved iron (dFe) is a key limiting micronutrient, but iron scavenging is observationally poorly constrained, leading to large uncertainties in the external sources of iron and hence in the state of the marine iron cycle. Here we build a steady-state model of the ocean's coupled phosphorus, silicon, and iron cycles embedded in a data-assimilated steady-state global ocean circulation. The model includes the redissolution of scavenged iron, parameterization of subgrid topography, and small, large, and diatom phytoplankton functional classes. Phytoplankton concentrations are implicitly represented in the parameterization of biological nutrient utilization through an equilibrium logistic model. Our formulation thus has only three coupled nutrient tracers, the three-dimensional distributions of which are found using a Newton solver. The very efficient numerics allow us to use the model in inverse mode to objectively constrain many biogeochemical parameters by minimizing the mismatch between modeled and observed nutrient and phytoplankton concentrations. Iron source and sink parameters cannot jointly be optimized because of local compensation between regeneration, recycling, and scavenging. We therefore consider a family of possible state estimates corresponding to a wide range of external iron source strengths. All state estimates have a similar mismatch with the observed nutrient concentrations and very similar large-scale dFe distributions. However, the relative contributions of aeolian, sedimentary, and hydrothermal iron to the total dFe concentration differ widely depending on the sources. Both the magnitude and pattern of the phosphorus and opal exports are well constrained, with global values of 8. 1 ± 0. 3 Tmol P yr−1 (or, in carbon units, 10. 3 ± 0. 4 Pg C yr−1) and 171. ± 3. Tmol Si yr−1. We diagnose the phosphorus and opal exports supported by aeolian, sedimentary, and hydrothermal iron. The geographic patterns of the export supported by each iron type are well constrained across the family of state estimates. Sedimentary-iron-supported export is important in shelf and large-scale upwelling regions, while hydrothermal iron contributes to export mostly in the Southern Ocean. The fraction of the global export supported by a given iron type varies systematically with its fractional contribution to the total iron source. Aeolian iron is most efficient in supporting export in the sense that its fractional contribution to export exceeds its fractional contribution to the total source. Per source-injected molecule, aeolian iron supports 3. 1 ± 0. 8 times more phosphorus export and 2. 0 ± 0. 5 times more opal export than the other iron types. Conversely, per injected molecule, sedimentary and hydrothermal iron support 2. 3 ± 0. 6 and 4. ± 2. times less phosphorus export, and 1. 9 ± 0. 5 and 2. ± 1. times less opal export than the other iron types.

Early Cretaceous magmatism and associated polymetallic mineralization in South China: the Tiantang example

ABSTRACTThe Tiantang Cu–Pb–Zn polymetallic deposit in western Guangdong, South China, is hosted in the contact zone between the monzogranite porphyry and limestone of the Devonian Tianziling Formation. Orebodies occur in the skarn and skarnized marble as bedded, lenses, and irregular shapes. In this study, we performed LA-ICP-MS zircon U–Pb dating, zircon trace elements, and Hf isotopic analyses on the Tiantang monzogranite porphyry closely related to Cu–Pb–Zn mineralization. Twenty-two zircons from the sample yield excellent concordia results with a weighted mean 206Pb/238U age of 104.5 ± 0.7 Ma, which shows that the emplacement of the monzogranite porphyry in the Tiantang deposit occurred in the Early Cretaceous. The zircon U–Pb age is largely consistent with the sulphide Rb–Sr isochron ages, indicating that both the intrusion and Cu–Pb–Zn mineralization were formed during the Early Cretaceous in South China. The εHf(t) values of three inherited zircons from the monzogranite porphyry are 13.1, 11.9, and 12.9, respectively, and the two-stage Hf model ages are 1096 Ma, 1087 Ma, and 1055 Ma, respectively. Except for the three inherited zircons, all εHf(t) values of zircons are negative and have a range of −7.6 to −3.4, with the two-stage model ages (TDM2) of 1380–1643 Ma, which indicates the rock-forming materials were mainly derived from the partial melting of Mesoproterozoic to Neoproterozoic crust rocks, and probably included some Neoproterozoic arc-related volcanic-sedimentary materials. In this study, the monzogranite porphyry from the Tiantang deposit has calculated Ce4+/Ce3+ ratios of zircon ranging from 91 to 359, indicative of a more oxidized signature and significant prospecting potential for ore-related magmatism. Based on ore deposit geology, isotope geochemistry, and geochronology of the Tiantang Cu–Pb–Zn deposit and regional geodynamic evolution, the formation of Early Cretaceous magmatism and associated polymetallic mineralization in South China is believed to be related to large-scale continental extension and subsequent upwelling of the asthenosphere.

West wall structuring of equatorial plasma bubbles simulated by three-dimensional HIRB model

Plasma density depletions in the equatorial ionosphere, or so-called equatorial plasma bubbles (EPBs) are generated in the post-sunset period and tend to have a very complex spatial structure. Especially, the east-west asymmetry of EPBs has been reported by various observations. Using a high-resolution bubble (HIRB) model, which is a newly developed three-dimensional numerical model for the equatorial ionosphere, small-scale structuring at the west wall of large-scale F-layer upwelling is clearly reproduced for the first time. It is not an eastward neutral wind but a vertical shear of zonal plasma drift velocity at the bottomside of the F region that plays an important role in accelerating the instability growth at the west wall and generating the east-west asymmetry of EPBs.

Does large woody debris affect the hyporheic ecology of a small New Zealand pasture stream?

Rehabilitation of vertical hydrological exchange in small pasture streams is expected to improve hyporheic habitat, invertebrate life and ecosystem functioning, and may be achieved by adding large woody debris (LWD). This study investigated whether hyporheic improvement within 10 to 50 cm below streambed surface is evident around existing wood structures in a small New Zealand pasture stream in the Whatawhata area near Hamilton. Samples were taken around LWD and from areas where no wood was present in the pasture and from a control stream. At the pasture stream site, where the hyporheic zone was impacted by sedimentation and suffered from low dissolved oxygen (DO) levels (on average 8.4, 4.3 and 2.4 mg L−1 at 10, 30 and 50 cm depth, respectively), LWD was not associated with a significant improvement in vertical hydrological exchange, hyporheic habitat quality or invertebrate richness. However, higher densities in hyporheic invertebrates were found where LWD was present (100 vs. 56 individuals per L of sediment), in particular Leptophlebiidae and Oligochaeta. Potential pumping effects of LWD may have been hampered by large-scale deep groundwater upwelling in this reach. We conclude that in pasture streams where sedimentation is a legacy of land clearance on unstable slopes and where low hyporheic DO concentrations prevail, wood addition may not be an effective rehabilitation tool.

Neptune’s global circulation deduced from multi-wavelength observations

We observed Neptune between June and October 2003 at near- and mid-infrared wavelengths with the 10-m W.M. Keck II and I telescopes, respectively; and at radio wavelengths with the Very Large Array. Images were obtained at near-infrared wavelengths with NIRC2 coupled to the adaptive optics system in both broad- and narrow-band filters between 1.2 and 2.2μm. In the mid-infrared we imaged Neptune at wavelengths between 8 and 22μm, and obtained slit-resolved spectra at 8–13μm and 18–22μm. At radio wavelengths we mapped the planet in discrete filters between 0.7 and 6cm.We analyzed each dataset separately with a radiative-transfer program that is optimized for that particular wavelength regime. At southern midlatitudes the atmosphere appears to be cooler at mid-infrared wavelengths than anywhere else on the planet. We interpret this to be caused by adiabatic cooling due to air rising at midlatitudes at all longitudes from the upper troposphere up to ≲0.1mbar levels. At near-infrared wavelengths we find two distinct cloud layers at these latitudes: a relatively deep layer of clouds (presumably methane) in the troposphere at pressure levels P∼300–≳600mbar, which we suggest to be caused by the large-scale upwelling and its accompanying adiabatic cooling and condensation of methane; and a higher, spatially intermittent, layer of clouds in the stratosphere at 20–30mbar. The latitudes of these high clouds encompass an anticyclonic band of zonal flow, which suggests that they may be due to strong, but localized, vertical upwellings associated with local anticyclones, rather than plumes in convective (i.e., cyclonic) storms. Clouds at northern midlatitudes are located at the highest altitudes in the atmosphere, near 10mbar.Neptune’s south pole is considerably enhanced in brightness at both mid-infrared and radio wavelengths, i.e., from ∼0.1mbar levels in the stratosphere down to tens of bars in the troposphere. We interpret this to be due to subsiding motions from the stratosphere all the way down to the deep troposphere. The enhanced brightness observed at mid-infrared wavelengths is interpreted to be due to adiabatic heating by compression in the stratosphere, and the enhanced brightness temperature at radio wavelengths reveals that the subsiding air over the pole is very dry; the relative humidity of H2S over the pole is only 5% at altitudes above the NH4SH cloud at ∼40bar. The low humidity region extends from the south pole down to latitudes of 66°S. This is near the same latitudes as the south polar prograde jet signifying the boundary of the polar vortex. We suggest that the South Polar Features (SPFs) at latitudes of 60–70° are convective storms, produced by baroclinic instabilities expected to be produced at latitudes near the south polar prograde jet.Taken together, our data suggest a global circulation pattern where air is rising above southern and northern midlatitudes, from the troposphere up well into the stratosphere, and subsidence of dry air over the pole and equator from the stratosphere down into the troposphere. We suggest that this pattern extends all the way from ≲0.1mbar down to pressures of ≳40bar.

Near-infrared spectroscopy of Miranda

Aims. We present new near-infrared spectra of the leading and trailing hemispheres of Uranus’s icy satellite Miranda. This body is probably the most remarkable of all the satellites of Uranus, because it displays series of surface features such as faults, craters, and large-scale upwelling, a remnant of a geologically very active past. Methods. The observations were obtained with PHARO at Palomar and SpeX at the IRTF Observatory. We performed spectral modelings to further constrain the nature and the chemical and physical states of the compounds possibly present on the surface of Miranda. Results. Water ice signatures are clearly visible in the H and K bands, and it appears to be found in its crystalline state over most of the satellite’s surface. Unlike what has been found for Uranus’s outer moons, we did not find any significative differences in the abundances of ices covering the leading and trailing hemispheres of Miranda. The signature of carbon dioxide cannot be seen in our spectra, which could still account for the presence of ammonia hydrate, though in small amounts.

Distinct Modes of Internal Variability in the Global Meridional Overturning Circulation Associated with the Southern Hemisphere Westerly Winds

Abstract The internal variability of the global meridional overturning circulation (GMOC) in long-term integration of the earth system model Community Earth System Models (COSMOS) is examined in this study. Two distinct modes of the GMOC, which are closely linked to the Southern Hemisphere westerly winds (SWW) anomalies, are found to vary on multidecadal and centennial time scales. The dominant mode is characterized by Southern Ocean dynamics: strengthening and poleward shift of the SWW associated with a positive phase of the southern annular mode yield Ekman-induced northward mass transport, including a zonally asymmetric response in the Southern Ocean sea surface temperature and a cooling in the tropical Pacific Ocean due to large-scale upwelling. The second mode projects mainly onto the Atlantic meridional overturning circulation (AMOC). It is driven by a combination of SWW variation and buoyancy forcing. Based on the relationship between the two modes together with the wind perturbation experiments, the authors emphasize that the full AMOC response to the SWW change takes several centuries in their model. The sea surface temperature in Northern Hemisphere high latitudes is significantly affected in this mode, showing a large-scale warming. Their results from a mid-Holocene experiment imply that both modes are independent from the climate background conditions in the Holocene. Finally, the authors argue that the natural modes of GMOC are important to understand trends in ocean circulation, with consequences for heat and carbon budgets for past, present, and future climate.

Spatiotemporal variability of satellite-derived colored dissolved and detrital organic materials in the South China Sea from 1997–2007

The dominant spatial patterns and temporal variations of colored dissolved and detrital materials in the South China Sea were presented by Sea-viewing Wide Field-of-view Sensor derived data from September 1997 to December 2007. Seasonal and interannual variations of colored materials in the South China Sea were discussed for the first time. Results showed that high values of these materials were mainly within the regions with large mixing and large-scale upwelling induced by a seasonally reversing monsoon (e.g. Gulf of Tonkin and northwest of Luzon Island in winter, southeast of Vietnam in summer, etc.) and in coastal regions, particularly in the estuaries of the rivers in summer (e.g. Pearl River and Mekong River). By contrast, low values were observed in the regions of downwelling (northwest of Luzon Island in summer) and deep basin regions in the South China Sea all throughout the year. This variability is highly correlated with that of chlorophyll a, except for at some costal regions, e.g. the Pearl River estuary, where the colored materials seldom co-vary with chlorophyll-a over an established threshold. High concentration of colored material will reduce photo-biological processes at these regions in some months. The main South China Sea is still below the critical value, when comparing with the thresholds of the seasonal colored material concentrations in the Sea. Such conclusions may be useful for the management of the South China Sea environments.

Shearwater Foraging in the Southern Ocean: The Roles of Prey Availability and Winds

BackgroundSooty (Puffinus griseus) and short-tailed (P. tenuirostris) shearwaters are abundant seabirds that range widely across global oceans. Understanding the foraging ecology of these species in the Southern Ocean is important for monitoring and ecosystem conservation and management.Methodology/Principal FindingsTracking data from sooty and short-tailed shearwaters from three regions of New Zealand and Australia were combined with at-sea observations of shearwaters in the Southern Ocean, physical oceanography, near-surface copepod distributions, pelagic trawl data, and synoptic near-surface winds. Shearwaters from all three regions foraged in the Polar Front zone, and showed particular overlap in the region around 140°E. Short-tailed shearwaters from South Australia also foraged in Antarctic waters south of the Polar Front. The spatial distribution of shearwater foraging effort in the Polar Front zone was matched by patterns in large-scale upwelling, primary production, and abundances of copepods and myctophid fish. Oceanic winds were found to be broad determinants of foraging distribution, and of the flight paths taken by the birds on long foraging trips to Antarctic waters.Conclusions/SignificanceThe shearwaters displayed foraging site fidelity and overlap of foraging habitat between species and populations that may enhance their utility as indicators of Southern Ocean ecosystems. The results highlight the importance of upwellings due to interactions of the Antarctic Circumpolar Current with large-scale bottom topography, and the corresponding localised increases in the productivity of the Polar Front ecosystem.

Spawning, larval abundance and growth rate of Sardinops sagax off southwestern Australia: influence of an anomalous eastern boundary current

The temporal and spatial distributions of sardine Sardinops sagax eggs and larvae off the oligotrophic southwestern coast of Australia were examined and related to gonadosomatic index, daily growth rates of larvae and regional biological oceanography. Seasonal environmental cycles were established from remotely sensed sea surface temperature and chlorophyll concentration, wind and sea surface height data. Sardine egg and larval distributions were determined from regular transect surveys and annual grid surveys. Sardine eggs and larvae were common across the continental shelf throughout the year between Two Rocks and Cape Naturaliste (~32 to 34° S), and gonadosomatic index data suggested a distinct winter peak in spawning activity. Surface chlorophyll concentrations were highest during winter, coincident with the seasonal peak in the southward flow of the Leeuwin Current along the continental shelf break. Retention conditions on the mid-outer shelf for pelagic eggs and larvae were therefore poor during this time. Egg and larval concentrations were lower than expected in winter and higher in summer when retention conditions were more favourable. Larval sardine growth rates were unexpectedly high, averaging 0.82 mm d -1 . Fisheries for clupeiod species off southwestern Australia are insignificant compared to other eastern boundary current systems. Our data suggest that this may be due to a combination of low primary productivity caused by suppression of large-scale upwelling by the Leeuwin Current and the modest seasonal maximum in primary productivity occurring during the time least favourable for pelagic larval retention.

Lateral and longitudinal patterns within the stygoscape of an alluvial river corridor

In landscape ecology, landscapes are viewed as hierarchically-organized groups of interacting components or zones. This perspective is applied in studies of riverscapes with increasing frequency,particularlyin studies ofchannel habitats and channel-floodplain interactions. Stygoscapes, the subsurface portions of riverscapes, have received less attention. Stygoscapes are composed of three saturated zones beneath and lateral to river channels: the hyporheic, parafluvial and riparian zones. These zones are differentiated on the basis of hydrological, biological and chemical conditions, and the degree of interaction with the channel surface. In this paper, we describe lateral and longitudinal patterns in the shallow (30 cm - 10 m depth) stygoscape of the alluvial Selwyn River, New Zealand. We used abutting hyporheic, parafluvial and riparian zones in large-scale downwelling (losing) and upwelling (gaining) sections of the river mainstem to compare physico-chemical and biological conditions across a broad stygoscape. The stygoscape zones had the same arrangement in both sections: hyporheic zones within the wetted channel, riparian zones furthest from the channel, and parafluvial zones between the hyporheic and riparian zones. Nitrate and dissolved reactive phosphorus concentrations and electrical conductivity were significantly higher, and dissolved organic phosphorus concentrations and pH levels lower, in the gaining section than the losing section. In both sections, ammonium, dissolved reactive phosphorus, and dissolved organic carbon concentrations and pH were higher in the hyporheic zone than the riparian zone. Within the losing section, DON and DOP concentrations were higher in the hyporheic zone than the riparian zone. Physico-chemical conditions were intermediate in the parafluvial zones of both river sections. These among-zone differences suggest that hyporheic zones are sinks for dissolved nutrients, and that effects of hyporheic sinks are greatest in losing river sections with unidirectional flow from the surface to the hyporheic zone. There were large differences among stygoscape zones in invertebrate assemblage composition, and smaller differences between the losing and gaining sections. Invertebrate densities, taxon richness and % insect taxa were higher in hyporheic zones than riparian zones. Invertebrate densities were intermediate in the parafluvial zones, and taxon richness and % insect taxa were similar in parafluvial and riparian zones. The spatial patterns we observed in the Selwyn River suggest that hydrological connectivity between zones, and permeability within zones, are among the most important determinants of chemical and biological dynamics in stygoscapes. Differences in large-scale upwelling and downwelling, and differences in water source (runoff and groundwater) appeared to be of secondary importance.